Conventionally, oxide superconductors including a high-temperature superconductor, such as a Y-Ba-Cu-O system superconductor, are prepared by either thoroughly blending together powdered materials in a proper blend ratio (e.g. Y:Ba:Cu=1:2:3), sintering a resultant blend at high temperature and holding it at high temperature in an oxygen atmosphere or blending together powdered materials and sintering a blend directly at high temperature in an oxygen atmosphere. The oxide superconductor thus manufactured is usually block-like in configuration. In practical application, the oxide superconductor needs to be formed into a wire, a ribbon, a thin film, an element and so on. However, it is substantially not possible to form these products from the aforementioned block-like unit.
In the formation of the ribbon, thin film and element, it is necessary to form a superconductive film on a substrate. This thin-film forming technique includes a plasma CVD, a thermal CVD, a sputtering, laser sputtering, and a technique for coating a slurry, that is a mixture of row materials with a solvent such as water, on a substrate. Various attempts have been made to apply the thin-film forming technique to, for example, various elements. For example, J. Narayan et al. Appl. Phys. Lett. 51(22) PP. 1845(1987) and D. Dijkkamp et al. Appl. Phys. Lett. 51(8) PP 619(1987) disclose a method for forming an oxide superconductor by a laser sputtering in a vacuum atmosphere. In this method, it is necessary to, subsequent to forming a thin film on a substrate, heat-treat it at a temperature as high as above 800.degree. C. in an oxygen atmosphere so that oxygen may be incorporated into a resultant crystal structure. However, there is a risk that the substrate prepared will be broken or oxidized so that it cannot be used in a practical application. Other thin-film forming methods also involves this problem, thus restricting the use of the substrate material in the formation of an oxide superconductor thin film. For example, an epoxy substrate for interconnection, an aluminum ribbon, a semiconductor substrate and an element-formed silicon substrate, upon being exposed to a high-temperature oxygen atmosphere, cannot be employed, failing to prepare an oxide superconductor thin film.
Forming an oxide superconductor thin film on a substrate, if possible, will find an extended application range for the oxide superconductor and offer a step forward to a further practical application.